Tool sections that are used in the hot stamping of metal sheets must be cooled, such as for instance by providing a cooling fluid through cooling channels that are formed within the tool sections. The cooling channels are in general conventionally machined, and typically they are drilled or milled during production of the tool. This production method limits homogeneous cooling when complex tool geometries are present.
It is known that thermal production methods are widely used in tool- and mould-making, due to ever shorter product development times and an increase in product variety for smaller lot sizes. For several years now metallic and non-metallic starting materials have been used, with the goal being to generate tools directly from computer assisted design (CAD) data. Such materials for tools, which are usually provided in powder form, are processed by laser-assisted methods. Laser generating and selective laser-sintering are two distinct examples of laser-assisted methods that are suitable for producing tools and moulds.
Laser generating can, in principle, be compared to a laser coating process, or also to laser build-up welding. In laser generating, the part to be produced is generated by partially or completely melting the starting material and successively adding individual sheets of coatings one on top of another. However, the level of accuracy that can be achieved using this method is too low to satisfy the requirements in regard to high-quality tools.
In selective laser-sintering, powder particles in a powder bed are partially melted or fused with the aid of a laser beam, and subsequently bind together to form a solid layer after cooling. Conventional selective laser-sintering systems include a laser, a beam-shaping and beam-guiding unit, a processor for software editing and processing, a unit for powder dosing, and a build platform. The laser beam is directed onto the build platform by way of a deflecting unit, for example a revolving mirror unit and an F-Theta lens. The processor unit controls the deflecting unit based on edited CAD data. The build platform carries the base on which the component is built up, and is designed to be leveling. Another option is to operate without the base, wherein the component is supported by the surrounding material. However, when using this method variant it must be ensured that the height of the build platform is adjustable. A likewise leveling powder reservoir and a wiper unit in the form of a blade or a roller are used to supply new material.
By repeating the process steps that are described below, a desired component can be generated, layer by layer. First, a desired powder layer thickness is applied, wherein a sufficient amount of powder for uniform coating should be available. The powder is applied across the entire surface of the build platform in a thickness of, for instance, 0.001 to 0.2 mm with the aid of a doctor blade or roller. The layers are incrementally sintered or fused into the powder bed by controlling the laser beam in accordance with the contour of the component. The build platform is then lowered slightly, and a new layer is applied. The powder is provided by raising a powder platform or as a supply in the doctor blade. The power density of the laser radiation that is used as the heat source is adjusted and supplied based on the powder system, in such a way that the developing temperature cycle partially fuses or melts a portion of the material, whereby the generated body is imparted structural strength.
To prevent oxidation of the melt, which adversely affects the sintering result, in particular in the case of metallic and ceramic starting materials, the selective laser sintering process is frequently carried out in the systems under inert gas or special metal gas atmospheres in a processing chamber.
A method for producing casting and pressing tools is known from US 2011/0229595 A1, which can be used to create free form heaters having appropriately arranged temperature control medium channels. With the aid of thermal spraying methods, a structure is created, which can comprise partially prefabricated temperature control channels. More particularly, thermal spraying is used to build a first insulating layer, and then either a lost mold or a prefabricated channel element is fixed to the first insulating layer. Additional insulating material is sprayed around the mold or channel element, and finally a machinable metal layer is applied. The process requires several steps to fabricate and position the lost mold or channel elements, to fix the lost mold or channel elements to the insulating layer, and to spray the various layers.
It would be beneficial to provide a method for making a tool that overcomes at least some of the above-mentioned disadvantages of the prior art.